(a) Field of the Invention
The present invention relates to a resource division, allocation, and transmitting/receiving method of downlink for reducing inter-cell interference in an orthogonal frequency division multiplexing system. More particularly, the present invention relates to a resource division, allocation, and transmitting/receiving method of downlink using an inter-cell interference eliminating scheme in an orthogonal frequency division multiplexing (hereinafter, referred to as “OFDM”) system, and a method for improving a system capacity and a data transmission speed of a cell-boundary mobile terminal using the same.
(b) Description of the Related Art
As electronic/communication technology has been rapidly developed, a wireless voice communication service and wireless Internet service has been provided using a wireless network. In order to provide such a wireless voice communication service and wireless Internet service, a mobile communication system uses a code division multiple access (CDMA) scheme, a frequency division multiple access (FDMA:) scheme, and a time division multiple access (TDMA) scheme.
When the mobile communication system uses the conventional FDMA or TDMA scheme, the mobile communication system may not use common resources between adjacent cells, and accordingly, a sufficient signal to interference ratio may be obtained. However, there is a problem in that a system capacity may be decreased due to low frequency reuse efficiency. Since such a FDMA or TDMA scheme is mainly designed to provide a voice service at a constant data rate, the system capacity may be increased by increasing the number of available channels of a sufficient signal to interference ratio by means of a power control.
In order to largely increase frequency reuse efficiency of such a FDMA or TDMA scheme, a CDMA-based voice system has been proposed. The CDMA scheme makes an interference amount of each channel to be less changed by averaging interference amounts, and accordingly, wholly more channel may undergo an appropriate interference.
However, as a main mobile communication service has been converted from the voice service of a constant data rate to a packet service of a variable data rate, the orthogonal frequency division multiplexing and multiple access (OFDM/OFDMA) scheme for easily avoiding interference has replaced the CDMA scheme for controlling interference by averaging interferences. However, the OFDM/OFDMA-based mobile communication system has a problem to manage interference between adjacent cells interference.
In the OFDM/OFDMA-based mobile communication system (hereinafter, referred to as ‘OFDM system’), the interference is averaged by a frequency hopping is proposed so as to manage such an interference between the adjacent cells interference problem. The frequency hopping spreads a frequency spectrum by hopping a transmit signal from one center frequency to another center frequency.
In the OFDM system, when each cell is designed to use different frequency hopping patterns, the inter-cell interference may be sufficiently averaged in an encoding packet.
As such an inter-cell interference averaging method, PCT published publication No. WO05/050873, entitled “resource partition, physical channel allocation and power allocation method, and a frequency reuse efficiency increasing method using the same in an orthogonal frequency division multiplexing access (OFDMA)-based cellular system” discloses that an interference is eliminated by averaging interferences so as to increase a frequency reuse, an entire resource is divided into a resource space and a resource sub-space, similar traffics are grouped, and the grouped traffics are allocated to one resource space and one resource sub-space. At this time, each resource area averages interference.
Describing this method in detail, in OFDM system, an entire cell is divided into three frequency reuse patterns and one resource space is divided into three resource sub-spaces. Each cell mainly uses one resource sub-space among the three resource sub-spaces to transmit data at a high power, and uses other two resource sub-spaces at a too low power to affect the adjacent cells. In this manner, the inter-cell interference may be averaged in the encoding packet.
Alternately, an inter-cell interference may be reduced by another method of “Interference Migration Considerations and Results on Frequency Reuse” (2005.6) by Siemens published in a 3GPP RAN WG1 Ad Hoc on LTE conferences. This paper proposes that a first reuse frequency is used between intra-cell mobile terminals and a second reuse frequency is used between cell-boundary mobile terminals. At this time, the intra-cell mobile terminals use some common resource among entire resources, and the cell-boundary terminals use other three-divided resources at each cell.
However, such a method has a problem in that a resource efficiency is decreased when the cell-boundary mobile terminal shares a resource with the intra-cell mobile terminals of the adjacent cell.
Meanwhile, the inter-cell interference of downlink is managed by decreasing a power of the base station largely affecting the mobile terminal. That is, the mobile terminal performs a communication when the power of the base station is decreased in a direction largely affecting the mobile terminal, and accordingly, it obtains a gain.
Since such an inter-cell interference management of downlink is based on interference directionality and interference convergence, a gain of downlink is small, a cell plane is complex, and resources are run by a plurality of resource group including a plurality of resources. And thus, when a normal cell structure is not provided, the mobile terminal is disposed near to the cell boundary line, or a density of the mobile terminal or traffic is not uniformly provided, a system capacity is decreased.
Accordingly, the OFDM system desires a method for solving an adjacent cell interference of the downlink so as to improve a transmission speed of a cell-boundary mobile terminal and increase a system capability.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.